Semiconductor integrated circuit

ABSTRACT

In a large scale integrated DRAM in pursuit of micro fabrication, data line-word line coupling capacitances are unbalanced between paired data lines. A data line-word line imbalance generates large noise when the data lines are subjected to amplification, which is highly likely to invite deterioration of very small signals on the data lines and erroneous amplification of data. One or a few of a plurality of word lines connected to a plurality of memory cells connected to one data line are alternately connected to subword driver arrays arranged on the opposing sides of a memory array. Positive and negative word line noise components cancel each other in the subword drivers when the data lines are subjected to amplification, so that the word line noise can be reduced. Therefore, signals read out by sense amplifiers can be prevented from deterioration thereby to increase the reliability of memory operation.

This is a continuation application of U.S. Ser. No. 10/155,085, filedMay 28, 2002 U.S. Pat. No. 6,625,051; which is a continuationapplication of U.S. Ser. No. 09/923,542, filed Aug. 8, 2001, now U.S.Pat. No. 6,426,889; which is a continuation application of U.S. Ser. No.09/532,734, filed Mar. 22, 2000, now U.S. Pat. No. 6,278,628.

FIELD OF THE INVENTION

The present invention relates to reduction of memory array noise in asemiconductor apparatus involving a memory array or arrays.

BACKGROUND OF THE INVENTION

The items of literature referenced in this specification are listedbelow, and they will be referenced by reference number. [Reference 1]:ITOH, K., Very Large Scale Integrated Memories, Baifukan, Nov. 5, 1994(1st edition), pp. 214–217, and [Reference 2]: K. Itoh, IEEE Journal ofSolid State Circuit, Vol. 25, No. 3, (1990); pp. 778–789 ([Reference 2]is the original work referenced in [Reference 1]).

[Reference 1] discusses noise arising via word lines when a dynamicrandom access memory (DRAM) is subjected to amplification. It furtherdiscusses, as a case of noise arising via word lines, the phenomenonthat a noise voltage on an unselected word line attributable to thecoupling capacitance of data lines and the word line gives rise to noiseon paired data lines. The impact of that noise is dependent on thestructure of the paired data lines (whether an open data Line structureor a folded data line structure) and the data line precharging system(whether a VD precharging system or a VD/2 precharging system). As aconclusion, it is stated that the use of a folded data line structureand a VD/2 precharging system helps reduce the noise.

The inventors pertaining to the present application for patent, beforefiling the application, studied indetail the occurrence of noiseattributable to the structure of a 1 Gb DRAM array using microfabrication technology of 0.16 to 0.13 μm and the coupling capacitanceof data lines and word lines. FIG. 10 illustrates a planar layout of theDRAM array studied before this application and part of a correspondingcircuit diagram. In the planar layout of (a), memory cells (MCs) aredisposed at prescribed intersections of data lines (DLs) and word line(WLs). This data line structure is a so-called folded data linestructure. Here are shown only the DLs for reading signals out of memorycells, the WLs serving as gates for selecting transistors, regions ofdiffused layer (ACTs), data line contacts (DLCTs) for connecting ACTsand DLs and storage node contacts (SNCTs) for connecting ACTs andstorage nodes of capacitors, but the storage nodes connected to theSNCTs are not shown. Above and underneath the memory array are arrangedan upper subword driver array (SWDA-U) and a lower subword driver array(SWDA-D), and two word lines WLs are alternately connected to the upperand lower subword driver arrays. Subword driver will be abbreviated toSWD below as required. To the left and right of the memory array aredisposed a left sense amplifier array (SAA-L) and a right senseamplifier array (SAA-R), respectively, and two data lines DLs arealternately connected to the left and right sense amplifier arrays.Sense amplifier will be abbreviated to SA below as required.

These alternate arrangements of SWDs and SAs are intended to ease thetightness of their layout pitches. To look at the boundary between theSWDA-U and the memory array, for instance, there is seen a reiteratedpattern of two WLs each passing the boundary and entering the SWD (WL0,WL1, WL4 and WL5) and ones ending at the boundary (WL2, WL3, WL6 andWL7). Connection of WLs to the SWD in this manner makes possible easingof the layout pitch per SWD in the direction of data lines to anequivalent of two WLs. For the layout of the SAs as well, the alternatearrangement serves to ease the pitch in the direction of word lines totwo pairs of DLs (four DLs). Since memory cells are extremely small in aDRAM, the pitches of WLs and DLs are very fine. This means increaseddifficulty in laying out SWDs and SAs at prescribed pitches, andaccordingly the alternate arrangement can make an importantcontribution.

Now to look at the relationships of connection between the WLs and theSWD arrays, more specifically to two mutually adjoining memory cells MC0and MC1 which are connected to the DLOT, both the WL0 and the WL1connected to these cells are connected to the SWDA-U. On the other hand,to look at two other mutually adjoining memory cells MC2 and MC3connected to the DLOB, they also share the same DLCT, and both the WL2and the WL3 connected to these cells are connected to the SWDA-D.Therefore, in the layout of the memory array of FIG. 10, the WLsconnected to the two memory cells sharing the DLCT are connected to thesame SWD array. In an overall view of the memory array, as the patternshown in FIG. 10( a) is reiterated vertically and horizontally, all theWLs connected to the MCs connected to the DLOT (WL0, WL1, WL4 and WL5 inthe diagram) are connected to the SWDA-U, and all the WLs connected tothe MCs connected to the DLOB (WL2, WL3, WL6 and WL7 in the diagram) areconnected to the SWDA-D. Accordingly all the word lines connected tomemory cells connected to any one data line are connected to the samesubword driver array.

These relationships are represented in a circuit diagram which ispresented as FIG. 10( b). In a folded data line structure, memory cellsare connected to half of the intersections between data lines and wordlines. For instance, while the memory cell MC0 is connected between theDLOT and the WL0, no MC is connected between the DLOB and the WL0. An MCconsists of a selecting transistor TG and a cell capacitor CS. One ofthe electrodes of the CS is a plate PL, which is connected in commonwith other memory cells in the array. The other electrode of the CS isconnected to either one of the source or the drain of the TG, and theother of the drain or the source of the TG is connected to the DL. TheDLOT and the DLOB are paired and connected to the SA0 in the SAA-L, andthe DL1T and the DL1B are connected to the SA1 in the SAA-R. These SAsamplify a very small voltage difference generated between paired DLs bya signal from the memory cell to a higher level for one DL and to alower level for the other DL.

Only the parts of MC0, MC1, MC2 and MC3 FIG. 10 are enlarged, with theirenlarged layout is shown in FIG. 11( a) and their circuit diagram inFIG. 11( b). Parasitic capacitors emerging between the WLs and DLs ofthese MCs are also shown. Between the WL0 or WL1 and the DLOT arises aparasitic capacitance C00 or C01, respectively. Between the WL0 or WL1and the DLOB arises a parasitic capacitance C00B or C01B, respectively.Between the WL2 or WL3 and the DLOB arises a parasitic capacitance C02or C03, respectively. Between the WL2 or WL3 and the DLOT arises aparasitic capacitance C02B or C03B, respectively.

Cross sections A–A′, B–B′ and C–C′ of the parts pointed by arrows in thelayout of FIG. 11( a) are respectively illustrated in FIG. 12( a), (b)and (c). The cross sections in FIG. 12 refer to areas near the two wordlines WL0 and WL1 in the direction represented by arrows in FIG. 11( a).The ACT region on the substrate is the active region of the MOStransistor, while other parts on the substrate are device isolationregions. Over them are wired WLs and DLs, and the DLs are connected toACTs by oval DLCTs. SNs are storage nodes of cell capacitors CSs, andconnected to the ACTs by SNCTs. The upper electrodes PLs of the CSs arecommonly connected by cells in the array, and over them are arrangedtwo-layered metallic wires M2 and M3.

To compare C00 and C00B here, as shown in the cross section A–A′ of FIG.12( a), the DLCT0 connected to the DL0T passes between the WL0 and theWL1 very close to them. The distance between the DLCT0 and the WL0,where the memory cell is made by micro fabrication, is about 30 nm.Therefore, the C00, which is a capacitance between the DL0T and the WL0,is substantially determined by the part between the DL0T and the WL0.

On the other hand, as shown in the cross section B–B′ of FIG. 12( b),the DL0B merely passes above the WL0, and the C00B, which is thecapacitance between the DL0B and the WL0, is determined by theinterlayer distance between the DL and the WL, and is about 250 nm inthe 0.13 μm generation. Therefore, the C00B is far smaller than the C00;a detailed capacitance simulation has revealed that the COOB is about 1%against a C00 of 100%. Thus, as illustrated in FIG. 11( b), in a foldeddata line structure, although the coupling capacitance of the WL0 withrespect to the DL0T and the DL0B may appear balanced between the C00 andthe C00B, the C00 is predominantly great in a large scale integratedDRAM using small memory cells, resulting in an imbalance. Similarly, theC0, C02 and C03 are far greater than the C01B, C02B and C03B,respectively. In other words, the DL-WL coupling capacitance is great inthe presence of an MC between the DL and the WL, but negligibly small inits absence.

This imbalance in DL-WL coupling capacitance is a new problem which hasbecome actualized by the decrease in the thickness of the insulatingfilm parallel to the substrate relative to the thickness of theinterlayer insulating film in the direction normal to the substrate,which in turn has resulted from the large scale integration of the DRAM.In a memory array in which the DL-WL coupling capacitance is unbalanced,WL noise posses a problem as will be described below.

FIG. 13 illustrates the memory array of FIG. 10 and a data pattern in acase wherein the word line noise reaches its peak. The WL0 through theWL7 are connected to the SWD0 through the SWD7, respectively; the SWD0,SWD1, SWD4 and SWD5 are arranged in the SWDA-U; and the SWD2, SWD3, SWD6and SWD7 are arranged in the SWDA-D. The DL0T and DL0B are connected tothe SA0 in the SAA-L, and the DL1T and DL1B are connected to the SA1 inthe SAA-R. The circuit diagram of the SAs is presented as FIG. 14( a),and the operating wave forms of the array are shown in FIG. 14( b).

Now is considered with reference to FIG. 13 a case in which the WL0 isselected. Other WLs than the WL0 in the array are connected to either aVSSU or a VSSD by an N-channel MOS transistor in the SWD. As illustratedin FIG. 14( b), every SWD's output is 0 V during standby. In each MC,the selecting transistor is turned off, and a voltage of VDL (e.g. 1.8V) or VSS (e.g. 0 V) is written into the capacitor according toinformation. In each SA, the SHRU and SHRD are at VPP (e.g. 3.5 V), theCS and CSN are at VBLR (e.g. 0.9 V), the BLEQ is at VPP, and the YS is 0V, while the DL is precharged to a potential of VBLR.

When a bank activate command and an address entered into the DRAM, ifthe memory array illustrated here is selected, the SHRL and BLEQ will bereduced to 0 V, and the precharging is interrupted, followed by theactivation of the WL0 to 3.5 V in the SWD0. Then the selectingtransistor of the MC leading to the WL0 is turned on, and signals emergefrom the cell capacitor to the DL0, DL1 and so forth. It is supposed nowthat low level (L) signals to all the 1024 pairs or 2048 units of T sideDLs from DL0T through DL1023T except the DLnT, and a high level (H)signal appears only to the DLnT. Then, since no signals emerges to theother DLs, from DL0B through DL1023B, they remain at 0.9 V. Thispattern, or a pattern inverted with respect to H and L, is the worstcondition in which the WL noise is at its greatest. Then, as the SA isactivated by driving the CSN to 0 V and the CSP to 1.8 V, all the DLsfrom DL0T through DL1023T except DLnT are amplified to 0 V, and all theDLs from DLOB to DL1023B except DLnB are amplified to 1.8 V.

How this takes place is illustrated in FIG. 13. The circled Ls above theDL0T and the DL1T indicated that the DL0T and the DL1T are amplified to0 V, and the circled Hs above the DL0B and the DL1B indicate that theDL0B and the DL1B are amplified to 1.8 V. The noise then arising on theWL0 will be as follows. The WL0 receives negative noise from the datalines from DL0T through DL1023T other than the DLnT via a couplingcapacitance. On the other hand, the WL0 receives positive noise from thedata lines from DL0B through DL1023B other than the DLnB via a couplingcapacitance. Whereas the noise arising on the WL0 will be the sum ofthese noise components, since the WL0 is connected to the MC which inturn is connected to the T side DLs from DL0T through DL1023T as statedabove, the WL0-DL0B coupling capacitance, for instance, is only about 1%of the WL0-DL0T coupling capacitance. Thus, the coupling capacitancebetween the WL0 and data lines on the B side is negligibly smaller thanthe coupling capacitance of data lines between the WL0 and the T side.Therefore, the negative noise arises almost uncanceled on the WL0. Thisis indicated by the circled minus signs above the WL0. Similarly,negative noise arises on the WL1, WL4 and WL5. Conversely, as the WL2,WL3, WL6 and WL7 are connected to the MC which in turn is connected tothe B side DLs from DL0B through DL1023B, the WL2-DL0T couplingcapacitance, for instance, is smaller than, only about 1% of, theWL0-DL0B coupling capacitance. Thus, the coupling capacitance betweenthe WL2 and data lines on the T side is negligibly smaller than thecoupling capacitance of between the WL2 and data lines on the B side.Therefore, positive noise arises on these WLs, which is indicated by thecircled plus signs above the WLs. In the waveform of FIG. 14( b) aswell, WL noise on the WL0, WL1 and WL2 is represented.

The noise having arisen here on the WLs will flow as an electric chargeto the VSS wires over the SWD through the channel MOS transistor in theSWD. As this VSS wiring in a DRAM extends for a few millimeters over theSWD from a bonding pad for voltage source in the middle of the chip toan end of the chip, it has a high impedance. Therefore, the noise havingarisen on a word line emerges as it is in the VSS on the SWD.

While this WL noise is positive on one half of all the WLs of the arrayand negative on the other half, the alternate connection of WLs to twoSWDs in the array of FIG. 13 results in the occurrence of negative noiseon every WL connected to the SWDA-U and of positive noise on every WLconnected to the SWDA-D. Therefore, the negative noise components havingarisen on the VSSU, which is the VSS wiring on the SWDA-U, reinforce oneanother, and the positive noise components having arisen on the VSSD,which is the VSS wiring on the SWDA-D, also reinforce one another.Accordingly these noise aggregates are very great. A detailed circuitsimulation has revealed that they are about 100 mV each. Furthermore,noise components having arisen on WLs take a long time to attenuatebecause they are not canceled until they reach the bonding pad forvoltage source in the middle of the chip.

This WL noise occurring during DL amplification returns to the DLs viathe WL-DL coupling capacitance, and invites erroneous actions. When an Hlevel signal emerges only on the DLnT as shown in FIG. 13, negativenoise components from the WL0, WL1, WL4, WL5 and so forth return to theDLnT. Also, positive noise components from the WL2, WL3, WL6, WL7 and soforth return from the DLnB. Thus, as viewed from the DLn pairs, noise inthe reverse direction to the desired signals return to reduce thequantity of signals. If the electric charge stored in the cell capacitorof the memory cell at the intersection between the WL0 and the DLnT hasbeen reduced by a leak or otherwise, there will be less of H levelsignals emerging at the DLnT when the WL0 is activated, so that this WLnoise will invert the data at the time of amplification. How this occursis illustrated in FIG. 14; the DLnT and DLnB are amplified in thedirection reverse to the minute difference in potential having arisen onthe DLnT and DLnB at the time of WL activation, inviting erroneousreading of data.

Thus, in the memory array of FIG. 10 studied before this application forpatent, as the WL noise components on word lines work in a direction ofreinforcing one another in the sense amplifier driver SWD in the worstcase, there is the problem of increased WL noise. This deteriorates thesignal read out by the sense amplifier, and accordingly destabilizes theoperation of the memory.

Therefore, an object of the present invention is to provide a highlyreliable memory array by reducing the noise arising on word lines whendata lines are subjected to amplification in a large scale IntegratedDRAM in pursuit of micro fabrication.

SUMMARY OF THE INVENTION

A typical means of the invention is summarized below. Every other orevery few of a plurality of word lines connected to a plurality ofmemory cells connected to one data line are disposed to be connected tosubword driver arrays arranged on the mutually opposite sides of amemory array. This disposition has an effect that, in the worst patternof word line noise in which all the other data line pairs than theaforementioned pair to be noted read out data reverse to those of thenoted pair, half of the word lines connected to receive positive noiseand the other half receive negative noise, so that noise components onthese word lines cancel each other on a ground level source line in thesubword driver array and are thereby reduced, Similarly, in the subworddriver array arranged along the other side of the memory array, half ofthe word lines connected to receive positive noise and the other halfreceive negative noise, so that noise components on these word linescancel each other on a ground level source line in the subword driverarray and are thereby reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A–1B of respectively illustrate a layout and a circuit diagram ofa first work line noise decreased memory array according to the presentinvention.

FIG. 2 illustrates a configuration of a DRAM chip.

FIG. 3 is a circuit diagram of a first subword driver arrangement foruse in the word line noise decreased memory array according to theinvention.

FIG. 4 is a diagram illustrating the principle of noise reduction by thefirst word line noise decreased memory array according to the invention.

FIG. 5A–5B respectively illustrate a layout and a circuit diagram of asecond word line noise decreased memory array according to theinvention.

FIG. 6A–6B respectively illustrate a layout and a circuit diagram of athird word line noise decreased memory array according to the invention.

FIG. 7A–7B respectively illustrate a layout and a circuit diagram of afourth word line noise decreased memory array according to theinvention.

FIG. 8 is a circuit diagram of a second subword driver for use in a wordline noise decreased memory array according to the invention.

FIG. 9 is a circuit diagram of a third subword driver for use in a wordline noise decreased memory array according to the invention.

FIG. 10A–10B respectively illustrate a layout and a circuit diagram of aDRAM memory array studied before this application for patent.

FIG. 11A–11B illustrate respective enlarged versions of the layout andthe circuit diagram of the memory cell of FIGS. 10A–10B.

FIG. 12A–12C illustrate respective cross sections of essential parts ofa memory in the memory array of FIGS. 11A–11B.

FIG. 13 is a diagram illustrating the principle of word line noise bythe memory array of FIG. 10.

FIG. 14A–14B respectively illustrate a circuit diagram and operatingwave forms of the sense amplifiers in the memory array of FIGS. 10A–10B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail below with reference to drawings. Although circuit devicesconstituting each block or the embodiments are not confined to specifictypes, they are formed over a single semiconductor substrate, such asone of single crystal silicon by a known circuit integrating technology,such as one for complementary MOS (CMOS) transistors or the like.Circuit symbols for metal oxide semiconductor field effect transistor(MOSFET) denote N-type MOSFETs (NMOSs) if without arrow, or P-typeMOSFETs (PMOSs) if with an arrow, except in FIGS. 3, 8 and 9 whereinNMOSs are marked with an arrow in a direction reverse to that for PMOSsto ensure clear distinction between NMOSs and PMOSs. In the followingdescription, MOSFETs may be referred to as MOSs for the sake of brevity.However, the present invention is not restricted to field effecttransistors (FETs) containing an oxide disposed between a metallic gateand a semiconductor layer, but it can be applied to FETs in generalincluding metal insulator semiconductor field effect transistors(MISFETs).

(Embodiment 1)

FIG. 1 shows a planar layout of a first word line noise decreased memoryarray according to the present invention and part of a correspondingcircuit diagram. In the planar layout of (a), a memory cell (MC) isarranged at each prescribed intersection of a data line (DL) and a wordline (WL). This layout shows only DLs for reading signals out of memorycells, WLs each constituting the gate of a selecting transistor, regionsof diffused layer (ACTs), data line contacts (DLCT) each for connectingan ACT and a DL, and storage node contacts (SNCTs) each for connectingan ACT and the storage node of a capacitor, but the illustration ofstorage node of capacitors to be connected to SNCTs is dispensed with.Essentially, one array has about 2048 DLs and about 512 WLs, but onlysome of them are shown here. Above and underneath the memory array arearranged an upper subword driver array SWDA-U and a lower subword driverarray SWDA-D, and two word lines WLs are alternately connected to theupper and lower subword driver arrays. To the left and right of thememory array are disposed a left sense amplifier array SAA-L and a rightsense amplifier array SAA-R, respectively, and two data lines DLs arealternately connected to the left and right sense amplifier arrays.

These alternate arrangements of SWDs and SAs are intended to ease thetightness of their layout pitches. To look at the boundary between theSWDA-U and the memory array, for instance, there is seen a reiteratedpattern of two WLs each passing the boundary and entering the SWD (WL1,WL2, WL5 and WL6) and ones ending at the boundary (WL0, WL3, WL4 andWL7). Connection of WLs to the SWD in this manner makes possible easingof the layout pitch per SWD in the direction of data lines to anequivalent of two WLs. Furthermore, while WL patterning requires a superresolution lithography such as phase shift lithography or off-axisillumination, connection of two mutually adjoining WLs to an SWD makesPossible connection of two WLs whose optical phases are inverse to eachother, and accordingly it is made easier to lay out the SWD.

For the layout of the SAs as well, the alternate arrangement serves toease the pitch in the direction of word lines to two pairs of DLs (fourDLs). Since memory cells are extremely small in a DRAM, the Ditches ofWLs and DLs are very fine. This means increased difficulty in laying outSWDs and SAs at prescribed pitches, and accordingly the alternatearrangement can make an important contribution.

Now to look at the relationships of connection between the WLs and theSWD arrays, the present invention is characterized by the relationshipof connection between alternately arranged SWD arrays and WLs. To lookat two mutually adjoining memory cells MC0 and MC1 which are connectedto the DL0T, these cells sharing a single DLCT, out of the WLs connectedto these cells, while the WL0 is connected to the SWDA-D, the WL1 isconnected to the SWDA-U. On the other hand, to look at two othermutually adjoining memory cells MC2 and MC3 connected to the DL0B, thesecells also sharing the same DLCT, out of the WLs connected to thesecells, while the WL2 is connected to the SWDA-U, the WL3 is connected tothe SWDA-D. Therefore, in the layout of the word line noise decreasedmemory array of Embodiment 1, the WLs connected to the two memory cellssharing the DLCT are connected to different SWD arrays.

In an overall view of the memory array, as the pattern shown in FIG. 1(a) is reiterated vertically and horizontally, half of the WLs connectedto the MCs connected to the DL0T (WL1 and WL5 in the diagram) areconnected to the SWDA-U, and the other half (WL0 and WL4 in the diagram)are connected to the SWDA-D. Further, half of the WLs connected to theMCs connected to the DL0B (WL2 and WL6 in the diagram) are connected tothe SWDA-U, and the other half (WL3 and WL7 in the diagram) areconnected to the SWDA-D. Accordingly, out of all the word linesconnected to memory cells connected to any one data line, half areconnected to one of the two subword driver arrays, and the other halfare connected to the other subword driver array. Furthermore, SWDs inthe SWDA-U are connected to VSSU, a common VSS line. Similarly, SWDs inthe SWDA-D are connected to VSSD, another common VSS line. Wiring of theVSSs in this manner makes it possible to cancel WL noise on the VSSs.

These relationships are represented in a circuit diagram which ispresented as FIG. 1( b). In a folded data line structure, memory cellsare connected to half of the intersections between data lines and wordlines. For instance, while the memory cell MC0 is connected between theDL0T and the WL0, no MC is connected between the DL0B and the WL0. An MCconsists of a selecting transistor TG and a cell capacitor CS. One ofthe electrodes of the CS is a plate PL, which is connected in commonwith other memory cells in the array. The other electrode of the CS isconnected to either one of the source or the drain of the TG, and theother of the drain or the source of the TG is connected to the DL. TheDL0T and the DL0B are paired and connected to the SA0 in the SAA-L, andthe DL1T and the DL1B are connected to the SA1 in the SAA-R. These SAsamplify a very small voltage difference generated between paired DLs bya signal from the memory cell to a higher level for one DL and to alower level for the other DL.

In this manner of connection, as will be explained in detail below, whenthe DL0T and DL0B are amplified by the SA0 to high and low levels,respectively, though negative noise arises on the WL0 and W01 andpositive noise arises on the WL2 and WL3, the positive and negativenoise components respectively arising on the WL1 and WL2 cancel eachother on the VSSU, which is a voltage source line on the SWDA-U.Similarly, the positive and negative noise components respectivelyarising on the WL0 and WL3 cancel each other on the VSSD, which is avoltage source line on the SWDA-D. Since WL noise components from a dataline pair cancel each other in the memory array according to theinvention, the noise canceling effect will not be affected by any datapattern that may arise on any other data line pair in the array.

The configuration of a DRAM using the word line noise decreased memoryarray according to the invention will be described below. FIG. 2illustrates the configuration of the DRAM chip. In the middle of thechip along the longer sides are disposed bonding pads (PADs) andindirect peripheral circuits (PERI1 and PERI2). In this section arearranged input/output circuits for addresses and data, a power circuit,a refresh control circuit, a main amplifier and so forth. Along theshorter sides are disposed array control circuits (A-CTLs) forcontrolling the SWDs and SAs. These circuits broadly divide the chipinto four blocks, which surround row decoders (R-DECs), each connectedto a main word line, and column decoders (C-DECs), each connected to acolumn selecting line. Each block is divided by sense amplifier arrays(SAAs) in the direction of rows and by subword driver arrays (SWDAs) inthe direction of columns. Each part surrounded by the SAAs and SWDs isthe memory array (MA) show in FIG. 1.

FIG. 3 illustrates a first subword driver (SWD) arrangement for use inthe word line noise decreased memory array according to the invention,shown in FIG. 1. In this SWD arrangement, every SWD in the same SWDarray (SWDA) is connected to a common grounding line VSSU. Further, asthe SWDs are alternately arranged relative to the memory array, on theboundary between the SWDA-U and the memory array it is found that someWLs (WL1, WL2, WL5 and WL6) pass the boundary and enter SWDs whileothers (WL0, WL3, WL4 and WL7) end at the boundary, the two differentpatterns alternating each other at every second WL. The WL noisedecreased memory array according to the invention is characterized bythe arrangement that half each of the WLs connected to the MCs connectedto the DL0T of FIG. 1 (WL1 and WL5) and the WLs connected to the MCsconnected to the DL0B (WL2 and WL6) is connected to an SWD in theSWDA-U.

To take up the SWD1 as an example, one SWD is composed of two N-channelMOS transistors MN1 and MN2 and one P-channel MOS transistor MP1. Thesources of the MN1 and MN2 are connected to the VSSU while their drainsare connected to the WL1. The gate of the MN1 is connected to the mainword line (MWLB), and that of the MN2 is connected to the FX1B. Thesubstrates (either the back gate or the well potential) of both the MN1and MN2 may be connected either to the VSSU as illustrated or to aseparately provided VBB line. The source of the MP1 is connected to theFX1, its drain to the WL1, and its gate to the MWLB. The substrate(either the back gate or the well potential) of the MP1 is connected tothe VPP (e.g. 3.5 V). Incidentally, the WLs of the memory array arrangedover the SWDA-U and those of the memory array underneath it areconnected to each other by the SWDA-U.

Hereupon, the operation that takes place when the MWLB and the FX1 areactivated and the WL1 is selected. In this case, the MWLB is at 0 V, theFX1 at 3.5 V, the FX2, FX5 and FX6 at 0 V, the FX1B at 0 V, and theFX2B, FX5B and FX6B at 3.5 V. At the SWD1, the MP1 is turned on, the MN1and MN2 are turned off to activate the WL1 to 3.5 V. On the other hand,at the SWD2, SWD5 and SWD6, the transistor corresponding to the MN1 isturned off, that corresponding to the MN2 is turned on, and the WL2, WL5and WL6 are connected to the VSSU (0 V). While the gate of thetransistor corresponding to the MP1 is at 0 V, as its source is also at0 V, the transistor is not turned on. Therefore, the WL2, WL5 and WL6which are unselected WLs are connected to the VSSU only by the MN2.

Other operating modes of the WL1 include (1) neither the MWLB nor theFX1 is selected and (2) the MWLB is unselected and the FX1 is selected.In (1) both the MN1 and MN2 are turned on and connected to the VSSU andin (2), only the MN1 is turned on and connected to the VSSU. The sameapplies to other SWDs as well.

Now will be described, with regard to the word, line noise decreasedmemory array according to the invention, the WL noise reducing effect inthe worst pattern wherein WL noise reaches its peak. What is consideredhere is a case in which, as shown in FIG. 4, low level (L) signalsemerge on all the 1024 pairs of or 2048 units of T side DLs from theDL0T through DL1023T, except the DLnT, and a high level (H) signalemerges only on the DLnT. This pattern, or the reversed pattern in termsof H and L, is the condition under which WL noise reaches its peak.Activation of SAs results in amplification of all the T side DLs fromDL0T through DL1023T except the DLnT to 0 V, and amplification of allthe B side DLs from DL0B through DL1023B except the DL0B to 1.8 V.Circled Ls over the DL0T and DL1T denote the amplification of the DL0Tand DL1T to 0V and the circled Hs above the DL0B and DL1B, theamplification of the DL0B and DLLB to 1.8 V. The noise arising on theWL0 then will be as described below. The WL0 receives negative noisefrom all the T side data lines from the DL0T through DL1023T1 except theDLnT via coupling capacitances. On the other hand, the WL0 receivespositive noise from all the B side data lines from the DL0B throughDL1023B except the DLnB via coupling capacitances. Whereas the noisearising on the WL0 will be the sum of these noise components, since theWL0 is connected to the MC which in turn is connected to the T side DLsfrom DL0T through DL1023T as stated above, the WL0-DL0B couplingcapacitance, for instance, is only about 1% of the WL0-DL0T couplingcapacitance. Thus, the coupling capacitance between the WL0 and datalines on the B side is negligibly smaller than the coupling capacitancebetween the WL0 and data lines on the T side. Therefore, the negativenoise arises almost uncanceled on the WL0. This is indicated by thecircled minus signs above the WL0. Similarly, negative noise arises onthe WL1, WL4 and WL5. Conversely, as the WL2, WL3, WL6 and WL7 areconnected to the MC which in turn is connected to the B side DLs fromDL0B through DL1023B, the WL2-DL0T coupling capacitance, For instance,is smaller than, only about 1% of, the WL2-DL0B coupling capacitance.Thus, the coupling capacitance between the WL2 and data lines on the Tside is negligibly smaller than the coupling capacitance between the WL2and data lines on the B side. Therefore, positive noise arises on theseWLs, which is indicated by the circled plus signs above the WLs.

As illustrated in FIG. 4, in the word line noise decreased memory arrayaccording to the invention, unlike in the memory shown FIG. 13 studiedbefore this application for patent, negative noise arises on one half ofthe WLs connected to the SWDA-U, and positive noise arises the otherhalf. Therefore, as the positive and negative noise components canceleach other on the VSSU, which is a voltage source line on the SWDA-U,the WL noise is reduced. At the same time, in the SWDA-D as well,negative noise arises on one half of the WLs connected to it, andpositive noise arises the other half. Therefore, as the positive andnegative noise components cancel each other on the VSSD, which is avoltage source line on the SWDA-D, the WL noise is reduced.

Thus, in the word line noise decreased memory array according to theinvention, signals of whatever pattern may emerge on data lines,positive and negative WL noise components work to cancel each other inthe SWDs when the data lines are subjected to amplification, so that theWL noise can be reduced. Therefore, signals read out by sense amplifierscan be prevented from deterioration thereby to increase the reliabilityof memory operation.

To note the quantity of signals emerging from memory cells, sincesmaller signals can be accurately sensed than by the memory array ofFIG. 10, a greater margin of operation can be allowed againstinsufficient capacitor capacitances of memory cells or a drop inelectric charges stored in the memory cell capacitors due to a leakcurrent.

Furthermore, this array is more tolerant to an imbalance between thecoupling capacitance between one of two data lines operating as a pairand one word line and that between the other data line and the same wordline. Accordingly, it is possible to shape the storage node contact ofeach memory cell ovally as shown in FIG. 1, and the process to linearlylay out the diffused layer is facilitated.

Thus by using the array according to the present invention, the refreshperformance of the DRAM can be improved. The manufacturing process ofthe DRAM can be facilitated, too.

(Embodiment 2)

A layout and a circuit diagram of a second word line noise decreasedmemory array according to the invention are shown in FIG. 5. Thisembodiment differs from Embodiment 1 in that, on the boundaries betweenSWD arrays and the memory array, WLs ending at a boundary and WLsconnected to an SWD array alternate each other at one line intervals.

Regarding this embodiment, too, the relationship of connection betweenWLs and the SWD arrays will be noted. To look at the MC0 and MC1, twomutually adjoining memory cells connected to the DL0T, they share thesame DLCT, but while the WL0, out of the WLs connected to these cells,is connected to the SWDA-U, the WL1 is connected to the SWDA-D. On theother hand, to look at the MC2 and MC3, two mutually adjoining memorycells connected to the DL0B, they also share the same DLCT, but whilethe WL2, out of the WLs connected to these cells, is connected to theSWDA-U, the WL3 is connected to the SWDA-D. Therefore, in the layout ofthe word line noise decreased memory array of Embodiment 2 as well, WLsconnected to two memory cells sharing the same DLCT are connected todifferent SWD arrays.

In this embodiment as well, in an overall view of the memory array, asthe pattern illustrated in FIG. 5( a) is reiterated vertically andhorizontally, half of the WLs connected to the MCs connected to the DL0T(WL0 and WL4 in the diagram) are connected to the SWDA-U, and the otherhalf (WL1 and WL5 in the diagram) are connected to the SWDA-D. Also,half of the WLs connected to the MCs connected to the DL0B (WL2 and WL6in the diagram) are connected to the SWDA-U, and the other half (WL3 andWL7 in the diagram) are connected to the SWDA-D. Therefore, out of allthe word lines connected to memory cells connected to any one data line,half are connected to one of the two subword driver arrays, and theother half are connected to the other subword driver array. Furthermore,SWDs in the SWDA-U are connected to VSSU, a common VSS line. Similarly,SWDs in the SWDA-D are connected to VSSD, another common VSS line.Wiring of the VSSs in this manner makes it possible to cancel WL noiseon the VSSs.

In the second word line noise decreased memory array according to theinvention, too, it is possible to cause positive and negative WL noisecomponents to cancel each other in the SWD when the data lines aresubjected to amplification, so that the WL noise can be reduced.Therefore, signals read out by sense amplifiers can be prevented fromdeterioration thereby to increase the reliability of memory operation.

(Embodiment 3)

FIG. 6 illustrates a layout and a circuit diagram of a third word linenoise decreased memory array according to the present invention. Thisembodiment differs from Embodiments 1 and 2 in that in that, on theboundaries between SWD arrays and the memory array, WLs connected to anSWD array and WLs ending at a boundary alternate each other at four lineintervals.

Regarding this embodiment, too, the relationship of connection betweenWLs and the SWD arrays will be noted. Both the WL0 and WL1 connected tothe MC0 and MC1, two mutually adjoining memory cells connected to theDL0T, are connected to the SWDA-U. On the other hand, both the WL2 andWL3 connected to the MC2 and MC3, two mutually adjoining memory cellsconnected to the DL0B, are also connected to the SWDA-U. Therefore, inthis embodiment, noise components arising on the WL0 and WL1 arecanceled on the VSSU by those arising on the WL2 and WL3. Similarly,noise components arising on the WL4 and WL5 are canceled on the VSSD bythose arising on the WL6 and WL7.

In this embodiment as well, in an overall view of the memory array, asthe pattern illustrated in FIG. 6( a) is reiterated vertically andhorizontally, half of the WLs connected to the MCs connected to the DL0T(WL0 and WL1 in the diagram) are connected to the SWDA-U, and the otherhalf (WL4 and WL5 in the diagram) are connected to the SWDA-D. Also,half of the WLs connected to the MCs connected to the DL0B (WL2 and WL3in the diagram) are connected to the SWDA-U, and the other half (WL6 andWL7 in the diagram) are connected to the SWDA-D. Therefore, cut of allthe word lines connected to memory cells connected to any one data line,half are connected to one of the two subword driver arrays, and theother half are connected to the other subword driver array.

In the third word line noise decreased memory array according to theinvention, too, it is possible to cause positive and negative WL noisecomponents to cancel each other in the SWD when the data lines aresubjected to amplification, so that the WL noise can be reduced.Therefore, signals read out by sense amplifiers can be prevented fromdeterioration thereby to increase the reliability of memory operation.

(Embodiment 4)

FIG. 7 illustrates a layout and a circuit diagram of a fourth word linenoise decreased memory array according to the invention. Thisembodiment, though its boundaries between the SWD arrays and the memoryarray are similar to those shown in FIG. 11, differs from Embodiments 1,2 and 3 in that the directions of the data line contacts DLCTs of theMC4, MC5, MC6 and MC7 in the memory cell array are altered so thatmemory cells whose diffused layers are aligned in the DL direction areconnected alternately to different DLs.

Both the WL0 and WL1 connected to the MC0 and MC1, two mutuallyadjoining memory cells connected to the DL0T, are connected to theSWDA-U. On the other hand, both the WL2 and WL3 connected to the MC2 andMC3, two mutually adjoining memory cells connected to the DL0B, are alsoconnected to the SWDA-U. Therefore, in this embodiment, noise componentsarising on the WL0 and WL1 are canceled on the VSSU by those arising onthe WL2 and WL3. The two mutually adjoining memory cells MC4 and MC5 arealso connected to the DL0B, with an oval DLCT being disposed towardunderneath the diffused layer, and the WL4 and WL5 connected to them areconnected to the SWDA-U. Similarly, the two mutually adjoining memorycells MC6 and MC7 are connected to the DL0T, with an oval DLCT beingdisposed toward underneath the diffused layer, and the WL6 and WL7connected to them are connected to the SWDA-U.

Therefore, in this embodiment, noise components arising on the WL0 andWL1 are canceled on the VSSU by those arising on the WL4 and WL5.Similarly, noise components arising on the WL2 and WL3 are canceled onthe VSSD by those arising on the WL6 and WL7.

In this embodiment as well, in an overall view of the memory array, asthe pattern illustrated in FIG. 7( a) is reiterated vertically andhorizontally, half of the WLs connected to the MCs connected to the DL0T(WL0 and WL1 in the diagram) are connected to the SWDA-U, and the otherhalf (WL6 and WLu7 in the diagram) are connected to the SWDA-D. Also,half of the WLs connected to the MCs connected to the DL0B (WL4 and WL5in the diagram) are connected to the SWDA-U, and the other half (WL2 andWL3 in the diagram) are connected to the SWDA-D. Therefore, out of allthe word lines connected to memory cells connected to any one data line,half are connected to one of the two subword driver arrays, and theother half are connected to the other subword driver array.

In the fourth word line noise decreased memory array according to theinvention, too, it is possible to cause positive and negative WL noisecomponents to cancel each other in the SWD when the data lines aresubjected to amplification, so that the WL noise can be reduced.Therefore, signals read out by sense amplifiers can be prevented fromdeterioration thereby to increase the reliability of memory operation.

(Embodiment 5)

This embodiment is a second subword driver (SWD) for use in the wordline noise decreased memory array according to the present invention.Although it is shown here in combination with the first word line noisedecreased memory array according to the invention, it is also applicableto other word line noise decreased memory arrays.

In the SWD illustrated in FIG. 8, the MWLB of FIG. 3 is divided into anMWLB0 and an MWLB1, and the number of FXs is halved to match thisdivision. This arrangement may enable the layout area of the SWDs to behalved. The SWDs are arranged in two tiers, and the VSS is divided intotwo, a VSSU1 and a VSSU2.

Where such SWDs are used, in order to eliminate WL noise, it isnecessary to connect to each VSSU an SWD matching both the WLs to beconnected to MCs to be connected to the DL0T and the WLs to be connectedto MCs to be connected to the DL0B. Thus, in the configurationillustrated in FIG. 8, as that in FIG. 1, the WL1 and WL5 are connectedto MCs to be connected to the DL0T. Further, the WL2 and WL6 areconnected to MCs to be connected to the DL0B. In such a case, byconnecting the SDW1 to which the WL1 is connected and the SWD6 to whichthe WL6 is connected to the VSSU1, WL noise components on these WLs canbe eliminated on the VSSU1. Further, by connecting the SDW2 to which theWL2 is connected and the SWD5 to which the WL5 is connected to theVSSU2, WL noise components on these WLs can be eliminated on the VSSU2.

Therefore, by the combined use of the subword driver and a word linenoise decreased memory array both according to the present invention, itis possible to cause positive and negative WL noise components to canceleach other in the SWD when the data lines are subjected toamplification, so that the WL noise can be reduced. Accordingly, signalsread out by sense amplifiers can be prevented from deterioration therebyto increase the reliability of memory operation.

(Embodiment 6)

This embodiment is a third subword driver (SWD) for use in the word linenoise decreased memory array according to the present invention.Although it is shown here in combination with the first word line noisedecreased memory array according to the invention, it is also applicableto other word line noise decreased memory arrays.

In the SWD illustrated in FIG. 9, a transistor corresponding to the MN2of the SWD1 in FIG. 8 is shared by the SWD1 and SWD6 and their WLs areconnected to each other. This arrangement enables the number oftransistors to be used by the SWDs to be reduced, and accordingly thelayout area of the SWDs can be reduced. The SWDs are arranged in twotiers, and the VSS is divided into two, a VSSU1 and a VSSU2, as in thearrangement of FIG. 8.

Where such SWDs are used, in order to eliminate WL noise, it isnecessary to connect to each VSSU an SWD matching both the WLs to beconnected to MCs to be connected to the DL0T and the WLs to be connectedto MCs to be connected to the DL0B. Thus, in the configurationillustrated in FIG. 9, as that in FIG. 1, the WL1 and WL5 are connectedto MCs to be connected to the DL0T. Further, the WL2 and WL6 areconnected to MCs to be connected to the DL0B. In such a case, byconnecting the SWD1 to which the WL1 is connected and the SWD6 to whichthe WL6 is connected to the VSSU1, WL noise components on these WLs canbe eliminated on the VSSU1. Further, by connecting the SWD2 to which theWL2 is connected and the SWD5 to which the WL5 is connected to theVSSU2, WL noise components on these WLs can be eliminated on the VSSU2.

Therefore, by the combined use of the subword driver and a word linenoise decreased memory array both according to the present invention, itis possible to cause positive and negative WL noise components to canceleach other in the SWD when the data lines are subjected toamplification, so that the WL noise can be reduced. Accordingly, signalsread out by sense amplifiers can be prevented from deterioration therebyto increase the reliability of memory operation.

In a word line noise decreased memory array DRAM according to theinvention, signals of whatever pattern may emerge on data lines,positive and negative WL noise components work to cancel each other inthe SWDs when the data lines are subjected to amplification, so that theWL noise can be reduced. Therefore, signals read out by sense amplifierscan be prevented from deterioration thereby to increase the reliabilityof memory operation.

Further to note the quantity of signals emerging from memory cells,since smaller signals can be accurately sensed than by a memory array inwhich DL-WL coupling capacitances are unbalanced, a greater margin ofoperation can be allowed against insufficient capacitor capacitances ofmemory cells or a drop in electric charges stored in the memory cellcapacitors due to a leak current. Therefore, by using the arrayaccording to the present invention, the refresh performance of the DRAMcan be improved. The manufacturing process of the DRAM can befacilitated, too.

1. A semiconductor device comprising: a sense amplifier; a memory array having a plurality of DRAM memory cells, a plurality of word lines and a plurality of data lines; a plurality of first drivers coupled to a plurality of first word lines, the plurality of first word lines being included in said plurality of word lines; a plurality of second drivers coupled to a plurality of second word lines, the plurality of second word lines being included in said plurality of word lines; a first line coupled to the plurality of first drivers and arranged to supply a first potential to the plurality of first drivers; and a second line coupled to the plurality of second drivers and arranged to supply the first potential to the plurality of second drivers; wherein said plurality of first drivers are formed on a first side of a substantially rectangular area where said memory array is formed, wherein said plurality of second drivers are formed on a second side of said substantially rectangular area, wherein said plurality of word lines cross a pair of data lines, said pair of data lines being two of said plurality of data lines which are coupled to said sense amplifier, wherein first and second DRAM memory cells are located between said pair of data lines and coupled to said plurality of first word lines, the first and second DRAM memory cells being included in said plurality of DRAM memory cells, wherein said first DRAM memory cells are coupled to one of said pair of data lines, wherein said second DRAM memory cells are coupled to the other of said pair of data lines, and wherein each of the plurality of memory cells is coupled to a corresponding one of the plurality of data lines via an oval contact.
 2. The semiconductor device according to claim 1, wherein the pair of data lines work as a pair for outputting information to said sense amplifier.
 3. The semiconductor device according to claim 1, wherein each of said plurality of DRAM memory cells has a transistor and a capacitor. 